This proposal entails the total syntheses of ophiobolin C, several 11-deoxyprostaglandins, the pyrethroids, and sarkomycin. Ophiobolin C is a representative member of a group of natural products (ophiobolins, cotylenins, fusicoccins, and ceroplastols) which have antibiotic, antifungal, plant growth stimulant, phytotoxic, and possibly insect chemical defense activity. The 11-deoxyprostaglandins have potent brochodilator activity. The pyrethroids are potent, naturally occurring, and environmentally compatible insecticides. Sarkomycin has antitumoral activity and is representative of a wider class of cytotoxic Alpha-methylene cyclopentanones. These compounds are all related by their availability from cyclobutanones via ring expansion. Specifically, a key reaction in the ophiobolin C synthesis will be the anionic oxy-Cope rearrangement of a substituted 6,7-divinylbicyclo[3.2.0]heptan-6-o1 to a bicyclo[6.3.0]undec-7-en-3-one. Subsequent cyclopentenone annulation via a Nazarov strategy followed by functional group modification will complete the synthesis. The cyclopentanones will be synthesized via a novel, one-carbon alkylative ring expansion of suitably substituted cyclobutanones. These syntheses are proposed to be highly convergent and efficient. For example, alkylative ring expansion of 2-(3-tetrahydropyranyloxy-1-octenyl)cyclobutanone with a suitable Alpha-lithioselenoxide is expected to produce directly a protected form of 11-deoxy PGE1 or 11-deoxy PGE2. A latent exocyclic methylene unit will be introduced via alkylative ring expansion of 2-vinylcyclobutanone, and after functional group modification, the exocyclic methylene will be revealed. It is anticipated that the proposed research will make significant contributions to medicinal and agricultural chemistry.